The Antitumor Assessment Core Facility was established in 2003 to provide expert support for early discovery of effective antitumor agents and therapeutics. The Core provides resources, professional and technical expertise and advisory services related to the evaluation of agents with potential therapeutic activity, and works closely with investigators to establish in vivo mouse models for the design and execution of pharmacokinetic, toxicity and In vivo efficacy studies. As such, the Core provides a major vehicle to facilitate pre-clinical studies and is a major contributor to the translational mission of the Center. The Core also determines the best formulation, administration route, and treatment schedule for each new compound, either alone or in combination with other agents. The Core helps investigators to design and plan their experiments, prepare animal protocols and grant applications involving animal studies, and analyzes and summarizes data for publication. Importantly, the Core acts as a central coordinator for studies involving support from several core facilities (including Animal Imaging, Comparative Pathology, Tissue Procurement Service, Analytical Pharmacology, Organic Synthesis, Microarray, Radiation Facility, and Cytology) so that studies are carried out properly and in a time- and cost-efficient manner. The services and collaborative work provided by the Antitumor Assessment Core has supported the research of 56 investigators from 9 programs. A particularly exciting example of the work supported is: in 2010 the Core provided support services that were used by Dr. Charles Sawyer's group (ET and CBEP Programs) to develop ARN-509, an Androgen Receptor (AR) inhibitor targeting castration-resistant prostate cancer (CRPC), the most advanced form of this disease. This study has led to a Phase l/ll Clinical Trial currently ongoing at MSKCC. The Core undertook all the animal studies performed at MSKCC for this work.